As an example of a vehicle brake device in which a braking force imparted to a vehicle is controlled in accordance with a brake pedal operation amount by a driver, vehicle brake devices disclosed, for example, in JP-A-2010-167915 (Patent Literature 1) and JP-A-9-328069 (Patent Literature 2) are known. In these vehicle brake devices, a braking force based on a controlled hydraulic pressure generated by an accumulator and an electromagnetic valve is imparted to wheel cylinders in response to the movement of an input piston.
However, when a power supply system fails, no electric power is supplied to the electromagnetic valve, and the servo pressure cannot be controlled. Namely, it is not possible to increase the servo pressure according to the operation amount of the brake pedal by electrically controlling the pressure. When this occurs, the braking force cannot be exhibited when the power supply fails.